Field of the Invention
The present invention relates to an apparatus for expanding a tube.
Published European Patent Application 0 468 076 A1 discloses an apparatus for expanding a tube, which includes a probe that can be introduced into the tube and has a radially expandable expansion sleeve made of an elastically deformable material. The expansion sleeve is braced by each of its ends on one shoulder of a receiving sleeve. The receiving sleeves are joined together by a tie rod and axially fixed in opposed directions. The tie rod is passed through the expansion sleeve and together with recesses in the expansion sleeves it forms annular recesses that each receive one end of the expansion sleeve. The expansion sleeve is acted upon over a portion of its inside surface with a pressure medium passing through bores in the tie rod. The expansion sleeve is provided with an annularly encompassing groove for receiving an O-ring on the outer periphery in the region of the end surface of the receiving sleeves, which end surface annularly surrounds the expansion sleeve. The O-rings are intended to guard the expansion sleeve against damage, should it be pinched into voids that are located between the receiving sleeves and the tube which is to be expanded, when pressure is imposed.
On one hand, the O-ring used in the known device must have adequate elastic properties in order to spring back to its original shape after the imposition of pressure. On the other hand, it must also have adequate mechanical strength in order to absorb axial forces that act upon it when pressure is imposed.
O-rings made of a material that is elastically deformable within the course of deformation until it rests against the inner wall of the tube, such as O-rings of a polymeric material, for example, are unable to absorb those high axial forces, so that when such O-rings are used, the expansion sleeve is pinched in an annular interstice between the tube and the receiving sleeve and can become irreversibly deformed as a result. That not only causes damage to the expansion sleeve but also makes it harder to recover the probe once the expansion has been accomplished.
However, if an O-ring of an inelastic material or a material with a small range of elasticity is used, there is the risk of permanent plastic deformation, which again means that the probe can only be recovered from the tube with very great difficulty, if at all.
It has been found that the contradictory demands for elasticity and strength of such a support ring can only be inadequately met, if at all, by all of the materials that may be considered.
In order to avoid the above-discussed problems, Published European Patent Application 0 314 267 A2, corresponding to U.S. Pat. No. 4,791,796, proposes using two metal support rings that are made of many segments which are displaceable relative to one another. Each of the rings is held together by an elastic ring and the rings are disposed side by side. Those segments can slide against one another on the former end surfaces which are then oriented toward one another, so that once the expansion sleeve has been expanded one of the support rings rests on the tube, while the other support ring rests on a shoulder serving as a boundary. As a result of the two support rings being disposed side by side and partly overlapping one another as seen in an axial plan view, the expansion sleeve is largely prevented from becoming pinched in the axial direction in the interstice between the tube and the expansion apparatus, or between the segments.